Sensory discrimination is the detail: not just that you were touched, but exactly what, where and how much. This episode is about why the brain needs that detail at all, and the answer is skilfulness. From finding the right coin in your pocket to fretting a guitar chord, we trace how discrimination feeds perception, perception couples with action, and that whole dance is what lets a child become skilful.
Sensory discrimination has been the backbeat to our first three episodes, so this time we put it front and centre. We start simply, discrimination is the precise detail your nervous system picks up, the location, the quality, the force, and then ask the real OT question: detail for the purpose of what? The answer is skilfulness. We use the coin-in-your-pocket and learning-the-guitar examples to show how haptic detail, touch and vision together, guides skill all day long, mostly without us thinking about it.
From there we get into the part that is hard to pull together from the literature: how sensory discrimination feeds perception, how perception couples with action through affordances, and how a child can only do with an object what their body can already embody. We talk about the error-detection loop that drives neuroplasticity, where skill breaks down for kids with sensory integrative difficulties, and why a child working hard just to stay upright against gravity may treat detail as irrelevant. It sets up the link to sensory modulation and safety, which is where we are headed next.
Lightly edited for readability. Speaker labels and chapter markers match the published episode.
Michelle: Hello. Hi Cory, hi Trace.
Cory: Hey guys, great to be with you again.
Michelle: Welcome everybody, joining Cory and my mentoring session with Tracy. We hope you are enjoying listening as we meander in and out of paediatric OT theory and practice. We are really on a journey to learn as much as we can about this huge, broad subject, trying to wrap our heads around it with what we already know and the new bits, and integrate it as much as we can. What you are listening to is not a lecture. There are lots of places, and we give you lots of resources, where you can go and hear that. This is us having read textbooks and been to lectures, now trying to integrate it into our own thinking. So you are seeing the gritty behind-the-scenes work. We apologise it is not neat and tidy, but that is how things go. So Cory, episode four, what are we revisiting today?
Cory: We were talking about posture, and that led us to praxis, and a backbeat to all of these topics was sensory discrimination. We alluded to it a few times, so we all thought we had better start talking about it, so you can understand how it underpins the subjects we are talking about and the function we are seeing in front of us.
Cory: Sensory discrimination is so big. If you want really detailed information about the structure and functions of each of the senses, purely neurologically, there are lots of places you can go. Tracy has told us about Principles of Neural Science, which is a beautiful, huge textbook, and some of the others we have mentioned, like Sensory Integration: Theory and Practice, give more of an overview. If you just want to dip your toes in, even Sensory Integration and the Child, the parent-based one, is a good way to get a sense of how each of the senses takes information from the environment and translates it into electrical signals to the brain. We will not dive into that process today, because we want to get to the juicy, meaty bits. I struggled when I first graduated to know the difference between sensory modulation and sensory discrimination. We have not talked about modulation yet, but we will, and I am hoping this helps people start to figure out the differences, because that takes time. So how do you put sensory discrimination together, Michelle? What do you think of when you think of it?
Michelle: I think about it as the detail. It is the noticing of a particular input, whether it is sight, hearing or touch, and knowing the exact features of it, the location and the detail. For touch, I can discern whether it is light or hard and I know what body part it is. So it is really the fine-tuning of it.
Cory: When I try to explain it to a parent, it is not just registering that I got touched somewhere on my body. It is my nervous system actually knowing what that was. Was it sticky, rough, hard, sharp? All the qualities of the input, and figuring out what it actually is. Tracy, I am sure you can help us refine this. Are we on the right track?
Tracy: You are spot on about sensory discrimination. It is the precise detail that is processed. But here is the OT question.
Tracy: Sensory processing for the purpose of what? Why does our brain need detail? Our brain needs detail so it can organise our system for skilfulness. If you pick up detail in any sensory system, the example most typically used is the touch system. Say you have some coins in your pocket and you are trying to find the coin that fits the parking meter. We do not really do that anymore, with credit cards and Venmo, but in the old days you reached into your pocket and got that just-right coin. You can tell the difference by feeling the size or the edge, maybe one has a rough edge and one is smooth, maybe one has a hole, maybe you can feel the weight. All that discernment of the quality of touch or weight is processed to tell you information, going from the touch receptors in your fingers up into your higher-level cortices, and it tells you information that is visual, even linked to language or cognition or memory, because you know the coin since you learned it. Your higher-level brain turns that into what we call representational information, and that connects to praxis, so you say, I do not want that coin, I want this one, and you isolate and pull the one you want right to your fingertips. Does that make sense?
Cory: It clearly popped into my head. When you feel a certain coin, you have language attached to that feeling and perception. I was even thinking of a fruit. If I picture the word orange, I can feel in my hand the rough texture of the skin, how hard it is to peel, and how squishy it is inside.
Michelle: I did the opposite. When Tracy was describing the coins, I saw a fifty cent, a dollar, so I had a visual image prompted by the touch detail.
Cory: I thought about the fifty cent piece too.
Tracy: That is it. When you combine somatosensory tactile input with visual information, the neurological word we use is haptic processing.
Tracy: Haptic detail guides so much of our skill all day long, and it lets you become efficient and automatic, so you do not have to think hard about things. Think about how you zip your coat. You do not even have to look, because you can feel when the zipper is engaged, and you know how to bilaterally shift your hands from holding to finessing to zipping. All those skilful daily living skills are what we are really interested in as occupational therapists. But when we work with children who have problems with coordination, very often their ability to pick up on that detail and operate on it is really weak. Dr Ayres made a very clear link between sensory discrimination and the functions of skilfulness that live under the big umbrella of praxis. Skilfulness is sometimes automatic, sometimes really practised, sometimes so effortful. If you are learning the guitar, how can you ever play if you cannot feel how your fingers have to go to each fret and each chord shape, how to configure your hand for the chord changes? That takes precise detail awareness in your hand, which guides the motor control, and then you add the finesse of rhythm and musicality. It all integrates, but it sits on this base of sensory discrimination.
Cory: You need really accurate feedback around how much pressure. With the guitar, if I cannot figure out how hard to push, I will not get a clear sound from the string. If I cannot tell whether I am pushing hard or soft, I cannot change the plan to make it work, I will just get a funky sound or buzzing, because the string is not pushed down against the fret.
Tracy: That is right, and the same with a zipper. You cannot get it to zip without the right amount of pressure, pinch, force and timing. All of those praxis functions depend on sensory discrimination.
Cory: Thinking about the pressure, putting the zip into the catch at the bottom, the sensations I need for that job, I am thinking proprioception and tactile.
Tracy: And if you do not have integration at the deepest level of somatosensation, tactile, proprioception and vestibular, then when you go to zip you will fall down, because you cannot maintain your core stability while moving your extremities with detail and precision. Dr Ayres got it right in terms of integration. It is a beautiful, precise system. As little kids develop, they play around with the feeling, the tactile discrimination, the grading and the timing. They push something hard, push it soft, push it just right, and get that nuance between too hard, too soft and just right. So much of our experience and skill comes through playing around with the feeling of it.
Michelle: The thing that just struck me, which I had not really thought about, is the background. Cory with the guitar will feel whether she has the pressure right, but at the start she should also hear that she has it right. The sound will not be right, which cues her in to change what she is doing. So while it is tactile input, the rest of the senses act like an orchestra to help add precision to that one system.
Tracy: Exactly. The sensory discrimination system works through precise mapping of the detail, but also through integration of the polysensory systems coming together, auditory and visual helping you. When you put your finger on the fret, the sound, the look and the feel all together help you know whether you got it right. If you got it wrong, the error gives a signal that needs correcting, and you correct the detail. That refinement is what leads to higher-level skilfulness. Sensory motor, embodied, through practice, is what leads to skill.
Cory: So in that process of error detection, adjustment, try again, got it right, is that the neuroplasticity, the pathways forming around that new skill?
Michelle: Exactly right. And vice versa: if I do not have precision in enough senses, I will not get that. If my auditory system cannot discriminate that the pitch was a smidge off, and my tactile system is not saying you are not quite right, then I will not correct, and I will keep repeating the activity in error.
Cory: You talked about typical development, Tracy. We do not come wired ready to be skilful, we are ready to become skilful but not yet skilful. So how do we discern when somebody is not detecting the error and not adjusting, and we go, that is not typical? How do you tell typical learning from something not coming together as it should, and then support it?
Michelle: I think we see it. You were spot on with posture, Cory, talking about the quality of it. We often hear parents say, oh yes, they hit the milestones, they did all of that, but they present with not enough quality of skill.
Cory: So with a really little child, is it more in the error detection, that they will not detect the errors, and then you start to become concerned, because it would not improve or progress, it would look clunky? Tracy, what do you think?
Tracy: That is exactly right. When a child produces an error, a lay observer or a parent may notice it looks a little off. What studying this theory and working on our clinical reasoning gives us is the ability to attune our eyes to where in that process the error, the clunkiness, the lack of ease and automaticity, is coming from. That is part of your journey as a clinician. You are observing where the detail is missing. Say a child is trying to put a thread into a needle, or kick a ball into a goal. Those are the same skill, one fine motor and one gross motor: take this thing and put it into that thing. If the issue is more that they do not understand what part of their finger to hold it with, so they use the more primitive parts of their hand, then giving them something bigger they can feel better will probably help them learn the feeling for the doing faster than continuing to be frustrated. OTs are really good at grading the shape, size and feel of things, and what we are talking about is why we do that task analysis, to give the fuel, the sensory discrimination detail, as the agent of precision and skilfulness.
Cory: That has been really helpful, Tracy. But if you grade the size of the bead up for a kid who still cannot figure out how the string goes into the bead, how do we work out where the problem lies?
Tracy: This takes us to the coolest thing, which is not easy to access in the literature, but here we go.
Tracy: Sensory discrimination is the foundation of praxis. Dr Ayres wrote that, and we have talked about it for decades, but the link between the two is how sensory discrimination leads to perception, and perception is coupled with action to give us praxis. Perception and action together are a dynamic system produced by the affordances of the body interacting with the environment. Think about a round object. If a human comes up to a round object, they know the roundness, the affordance of it, is something that can move across space. Put your hand on it and push, and it rolls. If you can balance on one foot, you can lift your foot and have it be the pusher or kicker. Our hands can be pushers, pullers, pick-uppers, our feet can be pushers, tappers, kickers, lifters. Those are actions our body can create, those are affordances, and they interact with the affordances out in the environment. If you give a big bead with a hole in it to kids and do not give them something to fill it with, they will fill it, by looking through it, blowing through it, interacting with the affordance of the hole. Give them a string and a bead, and they might see those two things can interact, and if they have the fine motor capacity, they will put them together. But give a bead and string to a baby who does not yet have the skill, and they will not see it as an option for their action, because they cannot embody putting it together. They will play with the string and the bead, but not put them together. Once the skill is in them, that becomes an action they can produce, a skill that is possible, because the affordance draws it out of them.
Cory: My brain is a little blown, this is so cool. I have to have the capacity in my body to do the action, so the baby does not have the fine motor capacity to put the thread through. But at a developmental point, babies start to put things into things, so how does that come together, cognitively, posturally, all the development to that point allowing them to perceive that this is something that can fit inside that thing?
Michelle: I am putting it together as a dance between the two: either cognitively or sensory-motorically, something develops that lets them hang on to something fine like a bead, and then they have the cognitive ability to do something with it. It might just accidentally happen the first time, then they repeat it, add to it, and file a memory of the repertoire they can do with it. As they move to the next level of development, with a ball they might catch it, roll it, kick it, and later balance it once their balance is fine-tuned enough. As they go through the stages they keep layering on.
Cory: So that is complicated, because if you do not have all these elements, the capacity in my body and the cognition, and I also have to fit in the perception piece, then at any point any of these pieces could undo the whole process. Is that right?
Tracy: That is exactly right, and it is a dynamic system. Cognition really results from the embodied experience. Once you embody it and can say, this is a thing that goes inside the thing, you have that as a schema. Affordance and action turn into schemas, and once you have schemas, I am capable of putting in, of pushing, of kicking, you forever own that. Like riding a bike, you cannot unlearn it, unless something degrades, or you fall off and bonk your head. You can lose skill through degeneration, injury or a degradation of memory. A tennis player who practises and practises will always be decent, but will not maintain expertise without practising, so you can have a degrading of skill, use it or lose it, but the basic schemas you do not really lose, they are episodic in memory. What we are really thinking about is how sensory discrimination is part of the perceptual affordance dance that builds the embodied cognitive and language capacity. Praxis is a capacity, language is a capacity, cognition is a capacity, and all of them draw from this rich sensory discrimination perceptual fund that gives you the possibilities. If I give you an object you have never seen before, you will explore it for its bits and parts, then turn it into something with meaningful, repetitive quality. If you have never seen a stretchy thing like a slinky, you notice it squeezes together and stretches apart, that if you put one part higher it flops around. We give children toys like that without obvious cause and effect, explore-this toys, and when you watch children play with them, you get a sense of their perception: do they just smash it hard, pick it up and toss it, act on it from an old schema, or generalise and generate new schemas, and how does that look in terms of smoothness, accuracy and timing? As you dance across that flow from perception into motor execution, you start to discern where the problem more likely comes from: the execution of motor function, or that they have no idea how to generate meaning out of the object. Children who line things up, for instance, get that this and this and this go next to each other to create a perceptual set, but do not move beyond perception into what those things are, whether they could be more meaningful than just the line. So you would work at that perceptual affordance level differently than if the child was lining things up to make them exactly even, working on precision. It comes down to observing what they are doing and using clinical reasoning, because we do not have tests for all of this. We have tests for sensory discrimination, playfulness, motor accuracy and motor execution, and we have the SIPT and the EASI and the world of Ayres sensory integration that help us get a sense of the process of praxis, but not great tests for all these parts. So it really comes down to clinical observation, reasoning and interpretation.
Michelle: So now I wonder, can we talk about sensory discrimination right down to the receptor level, the pathway heading up to the cortex? I am thinking about the tactile system, we will not go into detail. And then you said the word perception. Can we unpack that? We have the neural pathway for the sensory system, and then perception. Is that cognition? What is it?
Tracy: It is kind of the step between the pure sensory reception and the information landing in cortical areas. Because it is cortical, somebody may say, of course it is cognition. But there are steps where cognition sort of boils out of the embodiment and the integration. Cognition itself comes from perceptual embodiment, from experience, from putting the pieces together in an integrated way. So cognition is the summation function that becomes the representational holding tank of that information. That link between sensation, perception and cognition is pretty controversial depending on who you read, and it gets very detailed around top-down and bottom-up processing.
Michelle: At a neuroscience level, not an OT level.
Tracy: More at a neuroscience and psychological theory level. But for our purposes, looking at children, what we see is that they have to get this sensory detail and interact with it in a meaningful way for skilfulness to even be possible, and that breaks down for children with sensory integrative processing problems, so they are not able to make use of the detail. Where the problem comes from is not well understood, whether at the periphery, in the receptors, in the surround processing, or higher up in integration. It is probably at multiple levels and different for different children. For kids with known peripheral processing problems we know where it is coming from, but it does not just live at the peripheral level, because you see it higher up in processing and cognition. What we are really interested in is when a child is trying to learn to be an effective doer in the world: how to kick, use their hands to put coins in the bank, button their shirts, get food onto a fork and into their mouth, move food to the side to chew, or hear the difference between a pea and a bee, or a black bear. How do they create precision in their listening, speaking and doing? When children struggle with this, it is often because the sensory detail is not meaningful enough to them, so we have to enhance it. Or their nervous system is telling them the detail is not important, because they are working so hard just to keep themselves up against gravity that they do not care about detail.
Michelle: So it is second priority.
Tracy: Modulation problems, anxiety and postural problems can make sensory discrimination sort of irrelevant: I do not care where the hole is, because I am going to fall down if I try to put the thread through it. So part of deep clinical reasoning is figuring out where to start, whether we treat the postural problem first or the discrimination problem first. It is quite complex.
Cory: I am at the point where I have so many questions but cannot figure out what my question is. So maybe, for people listening, we can come back to this affordance thing, because I do not feel I have integrated it for myself yet. I am going to relisten to this episode, and we can revisit the concept, because it will be helpful to keep coming at it and putting it together. But if you are seeing a lack of skilful precision, or a child not knowing that a thing is something they can do with an object, what comes to mind for me is a kid on a swing not being able to figure out how to use their body to make the swing move.
Cory: In terms of the discriminative function of the vestibular system: once my body moves through space and gravity pulls differently at different points in the arc of the swing, especially at the point where it changes, that gives a signal to the vestibular system, which should discern what it is, and then you see the postural shift to know, I am now changing direction in space, so I am going to shift my weight to make the swing go. I threw in a random vestibular example even though we have not talked about that system this episode. What is actually going on in that shift?
Tracy: What you are describing is exactly how sensory discrimination leads to that sensory motor embodied, adaptive response, and that is where capacity grows out of. So much of our basic sensory motor experience grows out of that sensory discrimination signal. In the vestibular system, there is a signal of, am I in more flexion or extension in my head-neck complex as my body moves through space? If I get a vestibular and proprioceptive signal that I am in a little more flexion, I recruit the flexor surface, and counter it if I go too far by engaging my extensors. That is really what swinging is, that flow between flexion and extension. You do that in response to the sensory detail, and that discriminative detail helps organise your motoric, adaptive response in your postural motor system, so you become a swinger. Then you develop the schema of swinging, and now you are a swinger, a skill that grows out of swinging. That story repeats in every sensory motor domain. In the vestibular system it relates to adaptive responses like postural control, swinginess, bilaterality and balance, which all come out of the detail. In the somatosensory system, in your touch receptors, your discernment of the front or back of your thumb, the pressure you get in opposition, all that detailed discrimination gives you the ability to be a prehensile person who can pinch, pick up and move things, squeeze a grape and squish the juice out, or carefully pick it up so you do not. That precision is all guided by sensory discrimination. So in treatment, we are looking at giving that beautiful enhancement that fuels the sensory discrimination system with more information, detail, intensity, frequency or specificity, which gives you the adaptive connection: if I feel my fingers, I can be a careful picker-upper, but if I cannot feel my fingers, I will not be very skilful. It is all the same story, it just goes across the different systems.
Michelle: And that is where we can use the other systems to add emphasis, so that eventually things happen automatically, like putting a hand in your pocket and picking your coin with no thought. At the very start, what I might need to do is help the child notice all the different elements, sizes and shapes, using their vision, and narrate it so they get auditory input to help build the perception. So we layer attention onto the tactile system with details from other systems to emphasise the salient information, pay attention to this bit, and that helps refine the tactile functions, until eventually it is automated and we do not need to look or hear it.
Cory: In that example, you are pulling them in and helping them tune in through your relationship with the child, and also spotlighting the whole nervous system onto the function. We are enhancing the perception, but also saying, hey, pay attention, this is information, this is important and helpful, and then use it in a skilful way in the activity. So it is a combination: we enhance the actual sensory information, but also pull in the cognition piece around, this is useful, pay attention.
Tracy: That is exactly right.
Tracy: That affective spotlight, putting effort in, trying it again, doing it a little differently, all of those are the qualities that bring it into real cognition and real skill. It takes our affect, our connection to the child, our motivation with them and our attentional system together, working in mastery drive, really trying hard to get better at it. All of those qualities are part of the treatment, but we are also basing it in sensory discrimination for the purpose of that higher-level adaptive response. That is the formula that comes together in play so beautifully. If you do not know to enhance the sensation, you can play, but you will miss the beat of where the information is that the brain needs to do this with more fluidity, automaticity, ease and skilfulness. So it is really understanding the whole process, and the treatment planning is rich and exciting and fun, part of why we were having this conversation in the first place.
Michelle: And it keeps them from being reliant on somebody else. If we do not help facilitate them to do it for themselves, they will need a carer or a friend to say, tune in here, notice that. So it is about allowing them to be independent.
Cory: So much information, it has been so good. Key takeaways, I guess.
Cory: Key points from this episode. For me, my straightaway first thought was, I need to relisten to this episode, it is really complicated and it is exciting. What about you, Tracy?
Tracy: I have probably said this before, but Dr Ayres got it right yet again: sensory discrimination as the base of skilfulness and the base of praxis. There is such richness and truth there, and it still rings true today in the neurosciences, even 50 years later. That is critically important, and one of the reasons this treatment is efficacious and an evidence-based practice. Her brilliance really shines in terms of sensory discrimination.
Michelle: My mind has been blown. I will certainly be listening again and coming at this idea of affordances and perception, the orchestra of the brain. The thing that stuck out for me is that only when my body perceives itself to be safe, in my body or in relationship with you, can I worry about the detail. So I have to tend to first things first before we can get a child interested in detailing, finessing and fine-tuning.
Tracy: And on the other side of this coin, if your body cannot feel detail, it is really hard to feel safe. So sometimes the first step is, what is the container I am in, am I safe, can I feel it, do I know that? That leads us to how sensory discrimination and sensory modulation are partners, but different from each other, which comes full circle to how we started, Cory. Maybe next time we will jump into sensory modulation.
Michelle: You just segued us right there, Tracy.
Cory: Thanks, guys. We will get to talk to you soon. See you.
And that’s a wrap on today’s episode of Spirited Conversations. We hope this sparks something for you, whether it’s a new clinical idea, a fresh perspective, or just the reminder that you are definitely not alone in this work. If this conversation resonated, we would love for you to share it with anyone on their own learning journey. You can find information about the podcast on our website, and you can join us in the courses and communities the Developmental FX team have put together at developmentalfx.org. And if you’re enjoying listening, please subscribe or leave a review, it genuinely helps more people find us. Until next time, keep the conversations spirited!